Example systems and methods for testing materials and assemblies for voids, cracks, or other defects are provided. One example system for testing a part includes a chamber configured to accept the part, and a vacuum source connected to the chamber. The example system also includes a fluid source connected to the chamber and configured to provide a radioactive or isotope-labeled fluid to the chamber. In addition, the example system includes a detector configured to detect a presence or absence of radioactivity or the isotope-labeled fluid in the part.